/**
 *    Copyright 2009-2018 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.scripting.xmltags;

import java.lang.reflect.Array;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.builder.BuilderException;

/**表达式求值器，可参考ExpressionEvaluatorTest
 * 
 * @author Clinton Begin
 */
public class ExpressionEvaluator {

	/**表达式求布尔值，比如username == 'cbegin'
	 * @param expression
	 * @param parameterObject
	 * @return
	 */
	public boolean evaluateBoolean(String expression, Object parameterObject) {
		// 非常简单，就是调用ognl
		Object value = OgnlCache.getValue(expression, parameterObject);
		if (value instanceof Boolean) {
			// 如果是Boolean
			return (Boolean) value;
		}
		if (value instanceof Number) {
			// 如果是Number，判断不为0
			return new BigDecimal(String.valueOf(value)).compareTo(BigDecimal.ZERO) != 0;
		}
		// 否则判断不为null
		return value != null;
	}

	/**解析表达式到一个Iterable,核心是ognl
	 * @param expression
	 * @param parameterObject
	 * @return
	 */
	public Iterable<?> evaluateIterable(String expression, Object parameterObject) {
		// 原生的ognl很强大，OgnlCache.getValue直接就可以返回一个Iterable型或数组型或Map型了
		Object value = OgnlCache.getValue(expression, parameterObject);
		if (value == null) {
			throw new BuilderException("The expression '" + expression + "' evaluated to a null value.");
		}
		if (value instanceof Iterable) {
			return (Iterable<?>) value;
		}
		if (value.getClass().isArray()) {
			// 如果是array，则把他变成一个List<Object>
			// 注释下面提到了，不能用Arrays.asList()，因为array可能是基本型，这样会出ClassCastException，
			// 见https://code.google.com/p/mybatis/issues/detail?id=209
			// the array may be primitive, so Arrays.asList() may throw
			// a ClassCastException (issue 209). Do the work manually
			// Curse primitives! :) (JGB)
			int size = Array.getLength(value);
			List<Object> answer = new ArrayList<Object>();
			for (int i = 0; i < size; i++) {
				Object o = Array.get(value, i);
				answer.add(o);
			}
			return answer;
		}
		if (value instanceof Map) {
			return ((Map) value).entrySet();
		}
		throw new BuilderException("Error evaluating expression '" + expression + "'.  Return value (" + value + ") was not iterable.");
	}

}
